Implement AES-GCM cipher support (#630)

* Implement AES-GCM cipher support

Fixes #217.

A port of AES-GCM cipher support from Apache MINA-SSHD, based on apache/mina-sshd#132.

Included tests for decoding SSH packets sent from Apache MINA-SSHD and OpenSSH (Version 7.9p1 as used by Debian 10).

Manual tests also done on OpenSSH server 7.9p1 running Debian 10 with its available ciphers, including 3des-cbc, aes128-cbc, aes192-cbc, aes256-cbc, aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com and aes256-gcm@openssh.com.

* Changes per PR feedback

- Fixed variable/statement whitespaces and add back missing braces per coding standard requirement
- Moved Buffer.putLong() and Buffer.getLong() into GcmCipher.CounterGCMParameterSpec since it's the only user
- Moved BaseCipher.authSize into GcmCipher since it is the only cipher that would return a non-zero. BaseCipher will keep return 0 instead
- Made BaseCipher.cipher protected instead of making it publicly accessible
- Combined the three decoding modes in Decoder.decode() into one single method, to reduce code duplication
- Added integration test for the ciphers, along with the newly implemented AES-GCM ciphers

src/itest/docker-image/test-container/sshd_config

@@ -131,4 +131,6 @@ Subsystem	sftp	/usr/lib/ssh/sftp-server
 KexAlgorithms curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1,diffie-hellman-group-exchange-sha1
 macs umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-ripemd160-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com
 
-TrustedUserCAKeys /etc/ssh/users_rsa_ca.pub
+TrustedUserCAKeys /etc/ssh/users_rsa_ca.pub
+
+Ciphers 3des-cbc,blowfish-cbc,aes128-cbc,aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com

src/itest/groovy/com/hierynomus/sshj/transport/cipher/CipherSpec.groovy

@@ -0,0 +1,54 @@
+/*
+ * Copyright (C)2009 - SSHJ Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.hierynomus.sshj.transport.cipher
+
+import com.hierynomus.sshj.IntegrationBaseSpec
+import net.schmizz.sshj.DefaultConfig
+import spock.lang.Unroll
+
+class CipherSpec extends IntegrationBaseSpec {
+
+    @Unroll
+    def "should correctly connect with #cipher Cipher"() {
+        given:
+        def cfg = new DefaultConfig()
+        cfg.setCipherFactories(cipherFactory)
+        def client = getConnectedClient(cfg)
+
+        when:
+        client.authPublickey(USERNAME, KEYFILE)
+
+        then:
+        client.authenticated
+
+        cleanup:
+        client.disconnect()
+
+        where:
+        cipherFactory << [BlockCiphers.TripleDESCBC(),
+                          BlockCiphers.BlowfishCBC(),
+                          BlockCiphers.AES128CBC(),
+                          BlockCiphers.AES128CTR(),
+                          BlockCiphers.AES192CBC(),
+                          BlockCiphers.AES192CTR(),
+                          BlockCiphers.AES256CBC(),
+                          BlockCiphers.AES256CTR(),
+                          GcmCiphers.AES128GCM(),
+                          GcmCiphers.AES256GCM()]
+        cipher = cipherFactory.name
+    }
+
+}

src/main/java/com/hierynomus/sshj/transport/cipher/GcmCipher.java

@@ -0,0 +1,164 @@
+/*
+ * Copyright (C)2009 - SSHJ Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.hierynomus.sshj.transport.cipher;
+
+import net.schmizz.sshj.common.SSHRuntimeException;
+import net.schmizz.sshj.transport.cipher.BaseCipher;
+
+import javax.crypto.Cipher;
+import javax.crypto.SecretKey;
+import javax.crypto.spec.GCMParameterSpec;
+import java.security.GeneralSecurityException;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+
+public class GcmCipher extends BaseCipher {
+
+    protected int authSize;
+    protected Mode mode;
+    protected boolean initialized;
+    protected CounterGCMParameterSpec parameters;
+    protected SecretKey secretKey;
+
+    public GcmCipher(int ivsize, int authSize, int bsize, String algorithm, String transformation) {
+        super(ivsize, bsize, algorithm, transformation);
+        this.authSize = authSize;
+    }
+
+    @Override
+    public int getAuthenticationTagSize() {
+        return authSize;
+    }
+
+    protected Cipher getInitializedCipherInstance() throws GeneralSecurityException {
+        if (!initialized) {
+            cipher.init(mode == Mode.Encrypt ? Cipher.ENCRYPT_MODE : Cipher.DECRYPT_MODE, secretKey, parameters);
+            initialized = true;
+        }
+        return cipher;
+    }
+
+    @Override
+    protected void initCipher(Cipher cipher, Mode mode, byte[] key, byte[] iv) throws InvalidKeyException, InvalidAlgorithmParameterException {
+        this.mode = mode;
+        this.secretKey = getKeySpec(key);
+        this.parameters = new CounterGCMParameterSpec(getAuthenticationTagSize() * Byte.SIZE, iv);
+        cipher.init(getMode(mode), secretKey, parameters);
+        initialized = true;
+    }
+
+    @Override
+    public void updateAAD(byte[] data, int offset, int length) {
+        try {
+            Cipher cipher = getInitializedCipherInstance();
+            cipher.updateAAD(data, offset, length);
+        } catch (GeneralSecurityException e) {
+            throw new SSHRuntimeException("Error updating data through cipher", e);
+        }
+    }
+
+    @Override
+    public void update(byte[] input, int inputOffset, int inputLen) {
+        if (mode == Mode.Decrypt) {
+            inputLen += getAuthenticationTagSize();
+        }
+        try {
+            Cipher cipher = getInitializedCipherInstance();
+            cipher.doFinal(input, inputOffset, inputLen, input, inputOffset);
+        } catch (GeneralSecurityException e) {
+            throw new SSHRuntimeException("Error updating data through cipher", e);
+        }
+        /*
+         *  As the RFC stated, the IV used in AES-GCM cipher for SSH is a 4-byte constant plus a 8-byte invocation
+         *  counter. After cipher.doFinal() is called, IV invocation counter is increased by 1, and changes to the IV
+         *  requires reinitializing the cipher, so initialized have to be false here, for the next invocation.
+         *
+         *  Refer to RFC5647, Section 7.1
+         */
+        parameters.incrementCounter();
+        initialized = false;
+    }
+
+    /**
+     * Algorithm parameters for AES/GCM that assumes the IV uses an 8-byte counter field as its most significant bytes.
+     */
+    protected static class CounterGCMParameterSpec extends GCMParameterSpec {
+        protected final byte[] iv;
+
+        protected CounterGCMParameterSpec(int tLen, byte[] src) {
+            super(tLen, src);
+            if (src.length != 12) {
+                throw new IllegalArgumentException("GCM nonce must be 12 bytes, but given len=" + src.length);
+            }
+            iv = src.clone();
+        }
+
+        protected void incrementCounter() {
+            int off = iv.length - 8;
+            long counter = getLong(iv, off, 8);
+            putLong(addExact(counter, 1L), iv, off, 8);
+        }
+
+        @Override
+        public byte[] getIV() {
+            // JCE implementation of GCM will complain if the reference doesn't change between inits
+            return iv.clone();
+        }
+
+        static long addExact(long var0, long var2) {
+            long var4 = var0 + var2;
+            if (((var0 ^ var4) & (var2 ^ var4)) < 0L) {
+                throw new ArithmeticException("long overflow");
+            } else {
+                return var4;
+            }
+        }
+
+        static long getLong(byte[] buf, int off, int len) {
+            if (len < 8) {
+                throw new IllegalArgumentException("Not enough data for a long: required=8, available=" + len);
+            }
+
+            long l = (long) buf[off] << 56;
+            l |= ((long) buf[off + 1] & 0xff) << 48;
+            l |= ((long) buf[off + 2] & 0xff) << 40;
+            l |= ((long) buf[off + 3] & 0xff) << 32;
+            l |= ((long) buf[off + 4] & 0xff) << 24;
+            l |= ((long) buf[off + 5] & 0xff) << 16;
+            l |= ((long) buf[off + 6] & 0xff) << 8;
+            l |= (long) buf[off + 7] & 0xff;
+
+            return l;
+        }
+
+        static int putLong(long value, byte[] buf, int off, int len) {
+            if (len < 8) {
+                throw new IllegalArgumentException("Not enough data for a long: required=8, available=" + len);
+            }
+
+            buf[off] = (byte) (value >> 56);
+            buf[off + 1] = (byte) (value >> 48);
+            buf[off + 2] = (byte) (value >> 40);
+            buf[off + 3] = (byte) (value >> 32);
+            buf[off + 4] = (byte) (value >> 24);
+            buf[off + 5] = (byte) (value >> 16);
+            buf[off + 6] = (byte) (value >> 8);
+            buf[off + 7] = (byte) value;
+
+            return 8;
+        }
+    }
+}

src/main/java/com/hierynomus/sshj/transport/cipher/GcmCiphers.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright (C)2009 - SSHJ Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.hierynomus.sshj.transport.cipher;
+
+import net.schmizz.sshj.transport.cipher.Cipher;
+
+public class GcmCiphers {
+
+    public static final String GALOIS_COUNTER_MODE = "GCM";
+
+    public static Factory AES128GCM() {
+        return new Factory(12, 16, 128, "aes128-gcm@openssh.com", "AES", GALOIS_COUNTER_MODE);
+    }
+
+    public static Factory AES256GCM() {
+        return new Factory(12, 16, 256, "aes256-gcm@openssh.com", "AES", GALOIS_COUNTER_MODE);
+    }
+
+    /** Named factory for BlockCipher */
+    public static class Factory
+            implements net.schmizz.sshj.common.Factory.Named<Cipher> {
+
+        private int keysize;
+        private int authSize;
+        private String cipher;
+        private String mode;
+        private String name;
+        private int ivsize;
+
+        /**
+         * @param ivsize
+         * @param keysize The keysize used in bits.
+         * @param name
+         * @param cipher
+         * @param mode
+         */
+        public Factory(int ivsize, int authSize, int keysize, String name, String cipher, String mode) {
+            this.name = name;
+            this.keysize = keysize;
+            this.cipher = cipher;
+            this.mode = mode;
+            this.ivsize = ivsize;
+            this.authSize = authSize;
+        }
+
+        @Override
+        public Cipher create() {
+            return new GcmCipher(ivsize, authSize, keysize / 8, cipher, cipher + "/" + mode + "/NoPadding");
+        }
+
+        @Override
+        public String getName() {
+            return name;
+        }
+
+        @Override
+        public String toString() {
+            return getName();
+        }
+    }
+}

src/main/java/net/schmizz/sshj/DefaultConfig.java

@@ -18,6 +18,7 @@
 import com.hierynomus.sshj.key.KeyAlgorithm;
 import com.hierynomus.sshj.key.KeyAlgorithms;
 import com.hierynomus.sshj.transport.cipher.BlockCiphers;
+import com.hierynomus.sshj.transport.cipher.GcmCiphers;
 import com.hierynomus.sshj.transport.cipher.StreamCiphers;
 import com.hierynomus.sshj.transport.kex.DHGroups;
 import com.hierynomus.sshj.transport.kex.ExtInfoClientFactory;
@@ -171,6 +172,8 @@ protected void initCipherFactories() {
                 BlockCiphers.AES192CTR(),
                 BlockCiphers.AES256CBC(),
                 BlockCiphers.AES256CTR(),
+                GcmCiphers.AES128GCM(),
+                GcmCiphers.AES256GCM(),
                 BlockCiphers.BlowfishCBC(),
                 BlockCiphers.BlowfishCTR(),
                 BlockCiphers.Cast128CBC(),

src/main/java/net/schmizz/sshj/transport/Converter.java

@@ -45,6 +45,7 @@ abstract class Converter {
     protected long seq = -1;
     protected boolean authed;
     protected boolean etm;
+    protected boolean authMode;
 
     long getSequenceNumber() {
         return seq;
@@ -57,7 +58,11 @@ void setAlgorithms(Cipher cipher, MAC mac, Compression compression) {
         if (compression != null)
             compression.init(getCompressionType());
         this.cipherSize = cipher.getIVSize();
-        this.etm = mac.isEtm();
+        this.etm = this.mac != null && mac.isEtm();
+        if(cipher.getAuthenticationTagSize() > 0) {
+            this.cipherSize = cipher.getAuthenticationTagSize();
+            this.authMode = true;
+        }
     }
 
     void setAuthenticated() {